1. Field of the Invention
The present invention relates to a lens system suitable for use as an objective or taking lens for very compact photographic cameras whose diaphragm is arranged in front of the first lens element or behind the last lens element, the lens system providing a field coverage of at least 55 degrees and preferably 60 degrees or higher.
2. Description of the Prior Art
With the increasing demand for manufacturing smaller, more compact photographic cameras at a lower cost, there is an increased need for use of smaller and less costly lens systems. Triplet or a Tessar-type lens systems are good candidates for such use because these systems have relatively few lens elements.
Triplet-type or triplet derivatives such as Tessar-type lens systems or modified Tessar-type lens systems have been used in photographic apparatus for many years. Moreover, the objectives having a triplet type lens system with the diaphragm arranged either in front of the first lens element or behind the last lens element are also well known, and such lens systems are disclosed in U.S. Pat. No. 3,910,685, U.S. Pat. No. 4,886,342, U.S. Pat. No. 4,892,398, U.S. Pat. No. 4,836,665, U.S. Pat. No. 4,676,607, U.S. Pat. No. 3,967,884, U.S. Pat. No. 3,895,857, and U.S. Pat. No. 3,784,287. Such objectives have an advantage of being compact, having relatively few lens elements and eliminating the costs of "split" barrels.
However, many of these lens systems are assembled in their optical barrels with spacers such as spacer rings or shims placed between the optical components. This is disadvantageous because the spacers may cause tolerance build-up on thicknesses as well as tolerance build-ups due to spacer wedge. In addition, there is an increased cost due to extra parts.
The need for the spacers or shims can be eliminated as shown in U.S. Pat. No. 4,676,607, but if the edge contact is done inappropriately, the lens system may either become unnecessarily bulky, or may introduce unwanted stray light problems.
Finally, the inventors have found that if the sun's azimuth angle is 55 to 75 degrees, some of the sun light may propagate through a typical triplet type lens system causing glare in the film plane and causing some of the pictures taken by the end user to be of unacceptable image quality.
Thus, as there is a growing demand for more compact photographic cameras and correspondingly, there exists a need to further improve and simplify the lens system for use in such cameras, and to lower the cost of making such lens systems by making them less expensive to assemble while eliminating or minimizing stray light or glare problems and while maintaining or improving lens system imaging quality.